High temperature electrostatic chuck

ABSTRACT

A hot electrostatic chuck having an expansion joint between a chuck body and a heat transfer body. The expansion joint provides a hermetic seal, accommodates differential thermal stresses between the chuck body and the heat transfer body, and/or controls the amount of heat conducted from the chuck body to the heat transfer body. A plenum between spaced apart surfaces of the chuck body and the heat transfer body is filled with a heat transfer gas such as helium which passes through gas passages such as lift pin holes in the chuck body for backside cooling of a substrate supported on the chuck. The heat transfer gas in the plenum also conducts heat from the chuck body into the heat transfer body. The chuck body can be made of a material with desired electrical and/or thermal properties such as a metallic material or ceramic material. The chuck can be used in various semiconductor processes such as plasma etching, chemical vapor deposition, sputtering, ion implantation, ashing, etc. The ability to operate the chuck at temperatures in excess of 200° C. allows it to be used for plasma etching of noble metals such as Pt which require etching at high temperatures to volatilize low volatility etch products.

FIELD OF THE INVENTION

[0001] The invention relates to an electrostatic chuck (ESC) useful forprocessing substrates such as semiconductor wafers. The ESC can be usedto support a semiconductor substrate in a plasma reaction chamberwherein etching or deposition processes are carried out. The ESC isespecially useful for high temperature plasma etching of materials suchas platinum which are not volatile at low temperatures.

DESCRIPTION OF THE RELATED ART

[0002] Vacuum processing chambers are generally used for etching andchemical vapor depositing (CVD) of materials on substrates by supplyingan etching or deposition gas to the vacuum chamber and application of anRF field to the gas to energize the gas into a plasma state. Examples ofparallel plate, transformer coupled plasma (TCP) which is also calledinductively coupled plasma (ICP), and electron-cyclotron resonance (ECR)reactors are disclosed in commonly owned U.S. Pat. Nos. 4,340,462;4,948,458; and 5,200,232. Vacuum processing chambers are typicallydesigned to meet performance specifications which depend on the processto be carried out therein. Thus, the particular plasma generatingsource, vacuum pumping arrangement and substrate support associated withthe particular processing chamber must be customized or speciallydesigned to meet the performance specifications.

[0003] Substrates are typically held in place within the vacuum chamberduring processing by substrate holders. Conventional substrate holdersinclude mechanical clamps and electrostatic clamps (ESC). Examples ofmechanical clamps and ESC substrate holders are provided in commonlyowned U.S. Pat. No. 5,262,029 and commonly owned U.S. application Ser.No. 08/401,524 filed on Mar. 10, 1995. Substrate holders in the form ofan electrode can supply radiofrequency (RF) power into the chamber, asdisclosed in U.S. Pat. No. 4,579,618.

[0004] Substrates including flat panel displays and smaller substratescan be cooled by the substrate holder during certain processing steps.Such cooling is performed by the application of an inert gas, such ashelium, between the substrate holder and the opposed surface of thesubstrate. For instance, see U.S. Pat. Nos. 5,160,152; 5,238,499;5,350,479; and 5,534,816. The cooling gas is typically supplied tochannels or a pattern of grooves in the substrate holder and applies aback pressure to the substrate. Electrostatic chucks of the monopolartype utilize a single electrode. For instance, see U.S. Pat. No.4,665,463. Electrostatic chucks of the bipolar type utilize mutualattraction between two electrically charged capacitor plates which areseparated by a dielectric layer. For instance, see U.S. Pat. Nos.4,692,836 and 5,055,964.

[0005] Substrate supports for vacuum processing chambers are typicallymounted on a bottom wall of the chamber making servicing and replacementof the substrate support difficult and time consuming. Examples of suchbottom mounted substrate supports can be found in U.S. Pat. Nos.4,340,462; 4,534,816; 4,579,618; 4,615,755; 4,948,458; 5,200,232; and5,262,029. A cantilevered support arrangement is described in commonlyowned U.S. Pat. Nos. 5,820,723 and 5,948,704.

[0006] High temperature electrostatic chucks incorporating clampingelectrodes and heater elements have been proposed for use in chemicaldeposition chambers. See, for example, U.S. Pat. Nos. 5,730,803;5,867,359; 5,908,334; and 5,968,273 and European Patent Publication628644 A2. Of these, EP'644 discloses an aluminum nitride chuck bodyhaving an RF metallic electrode plate which is perforated with holes toform a mesh and a heater embedded therein, the chuck body beingsupported on an alumina cylinder such that the outer periphery of thechuck body extends beyond the cylinder. The '803 patent discloses achuck body of silicon nitride or alumina having an electrical grid ofMo, W, W—Mo and a Mo heater coil wire embedded therein, the chuck bodybeing supported by a Mo heat choke cylinder which surrounds a Cu or Alwater cooled cooling plate in thermal contact with the chuck body by athermal grease which allows differential expansion between the chuckbody and the cooling plate. The '359 patent describes a chuckoperational at temperatures on the order of 500° C., the chuck includingsapphire (single crystal Al₂O₃) layers brazed to opposite sides of aniobium electrode and that assembly brazed to a metal base plate. The'334 patent describes a chuck for use at temperatures in excess of 175°C., the chuck including polyimide films on either side of a monopolar orbipolar electrode with the lower polyimide film self adhered to astainless steel platen. The '273 patent discloses a layered chuck bodyincluding an aluminum nitride top layer, an electrode, an aluminumnitride layer, a metal plate, a heater, a metal plate and an aluminumcomposite, the chuck body being supported by a cylinder such that theouter periphery of the chuck body extends beyond the cylinder.

[0007] Some ESC designs use a heat conduction gas such as helium toenhance conduction of heat between adjacent surfaces of the wafersupport. For instance, U.S. Pat. No. 5,155,652 describes an ESC havinglayers including an upper pyrolytic boron nitride layer or optionallypolyimide, alumina, quartz, or diamond, an electrostatic pattern layercomprised of a boron nitride substrate and a conductive pattern ofpyrolytic graphite thereon, a heater layer comprised of a boron nitridesubstrate and a conductive pattern of pyrolytic graphite thereon, and aheat sink base of KOVAR (NiCoFe alloy with 29%Ni, 17%Co and 55%Fe). Theheat sink base includes water cooling channels in a lower portionthereof and chambers in an upper surface thereof which can be maintainedunder vacuum during heatup of the chuck or filled with helium to aid incooling of a wafer supported by the chuck. U.S. Pat. No. 5,221,404describes a support table comprised of an upper member which supports awafer and a lower member which includes a liquid passage for temperaturecontrol of the wafer, the upper member including an ESC constituted by acopper electrode between polyimide sheets and a gap between contactingsurfaces of the upper and lower members being supplied a heat conductiongas. Commonly owned U.S. Pat. No. 5,835,334 describes a high temperaturechuck wherein helium is introduced between contacting surfaces of alower aluminum electrode and an electrode cap which is bolted to thelower electrode, the electrode cap comprising anodized aluminum ordiamond coated molybdenum. A protective alumina ring and O-ring sealsminimize leakage of the coolant gas between the electrode cap and thelower electrode. The electrode cap includes liquid coolant channels forcirculating a coolant such as ethylene glycol, silicon oil, fluorinertor a water/glycol mixture and the lower electrode includes a heater forheating the chuck to temperatures of about 100-350° C. To preventcracking of the anodization due to differential thermal expansion, theelectrode cap is maintained at temperatures no greater than 200° C. Inthe case of the diamond coated molydenum electrode cap, the chuck can beused at higher temperatures.

[0008] International Publication WO 99/3695 describes a process forplasma etching a platinum electrode layer wherein a substrate is heatedto above 150° C. and the Pt layer is etched by a high densityinductively coupled plasma of an etchant gas comprising chlorine, argonand optionally BCl₃, HBr or mixture thereof. U.S. Pat. No. 5,930,639also describes a platinum etch process wherein the Pt forms an electrodeof a high dielectric constant capacitor, the Pt being etched with anoxygen plasma.

[0009] Although there has been some attempts to provide improved chuckdesigns for use at high temperatures, the high temperatures imposedifferential thermal stresses which are detrimental to use of materialsof different thermal expansion coefficients. This is particularlyproblematic in maintaining a hermetic seal between ceramic materialssuch as aluminum nitride and metallic materials such as stainless steelor aluminum. As such, there is a need in the art for improved chuckdesigns which can accommodate the thermal cycling demands placed uponhigh temperature chuck materials.

SUMMARY OF THE INVENTION

[0010] The invention provides an electrostatic chuck useful in a hightemperature vacuum processing chamber comprising a chuck body, a heattransfer body and an expansion joint therebetween. The chuck bodycomprises an electrostatic clamping electrode and optional heaterelement, the electrode being adapted to electrostatically clamp asubstrate such as a semiconductor wafer on an outer surface of the chuckbody. The heat transfer body is separated from the chuck body by aplenum located between spaced apart surfaces of the chuck body and theheat transfer body, the heat transfer body being adapted to remove heatfrom the chuck body by heat conductance through a heat transfer gas inthe plenum. The expansion joint attaches an outer periphery of the chuckbody to the heat transfer body, the expansion joint accommodatingdifferential thermal expansion of the chuck body and the heat transferbody while maintaining a hermetic seal during thermal cycling of thechuck body.

[0011] According to a preferred embodiment, the heat transfer bodycomprises a cooling plate having at least one coolant passage therein inwhich coolant can be circulated to maintain the chuck body at a desiredtemperature and the plenum is an annular space extending over at least50% of the underside of the chuck body. In this embodiment, the heattransfer body includes a gas supply passage through which heat transfergas flows into the annular space. According to a preferred embodiment,the chuck body includes gas passages extending between the plenum andthe outer surface of the chuck body. The gas passages can be provided inany suitable arrangement. For instance, if the outer portion of thechuck body tends to become hotter than the central portion thereof, thegas passages can be located adjacent to the expansion joint so that theheat transfer gas flows from the plenum to the underside of an outerperiphery of the substrate during processing thereof.

[0012] According to the preferred embodiment, the chuck body comprises ametallic material such as aluminum or alloy thereof or a ceramicmaterial such as aluminum nitride. In the case of a ceramic chuck body,the expansion joint can comprise a thin metal section brazed to theceramic chuck body. Lift pins can be used to raise and lower asubstrate. For instance, the heat transfer body can include lift pinssuch as cable actuated lift pins mounted thereon, the lift pins beingmovable towards and away from the chuck body such that the lift pinstravel through holes in the chuck body to raise and lower a substrateonto and off of the chuck body.

[0013] The expansion joint can include a mounting flange adapted toattach to the heat transfer body and a heat choke such as a single ormulti-piece flexible metal part. The heat choke can include inner andouter annular sections interconnected by a curved section, the innerannular section being attached to the chuck body and the outer annularsection being attached to the mounting flange. The expansion joint canalso include a connecting member such as a thin ring attached at one endto an outer periphery of the chuck body by a joint such as a mechanicaljoint or metallurgical joint such as a brazed joint, the connectingmember being of a metal having a coefficient of thermal expansion closeenough to that of the chuck body to prevent failure of the joint duringthermal cycling of the chuck body. Further, the expansion joint caninclude a thermal expansion section which abuts an outer edge of thechuck body, the thermal expansion section being thermally expandable andcontractible to accommodate changes in dimensions of the chuck body.

[0014] The chuck body can include a ceramic or metallic tubular sectionextending from a central portion of the underside of the chuck body suchthat an outer surface of the tubular section defines a wall of theplenum, the tubular section being supported in floating contact with theheat transfer body with a hermetic seal therebetween. The interior ofthe tubular section can include power supplies supplying RF and DC powerto the clamping electrode and AC power to the heater element, and/or atemperature measuring arrangement for monitoring temperature of thechuck body.

[0015] According to an embodiment of the invention, the chuck is areplaceable electrostatic chuck for a vacuum processing chamber whereinthe chuck includes a chuck body and an expansion joint. The chuckcomprises an electrode having an electrical contact attachable to anelectrical power supply which energizes the electrode sufficiently toelectrostatically clamp a substrate on an outer surface of the chuckbody. The expansion joint includes a first portion attached to an outerperiphery of the chuck body and a second portion removably attachable toa heat transfer body such that a plenum is formed between spaced apartsurfaces of the chuck body and the heat transfer body.

[0016] The invention also provides a method of processing a substrate ina vacuum process chamber wherein the substrate is electrostaticallyclamped on a chuck body comprising a clamping electrode and an expansionjoint attaching an outer periphery of the chuck body to a heat transferbody such that a plenum is formed between spaced apart surfaces of thechuck body and the heat transfer body, the method comprising clamping asubstrate on an outer surface of the chuck body by energizing theelectrode, supplying a heat transfer gas to the plenum, the heattransfer gas in the plenum passing through gas passages in the chuckbody to a gap between an underside of the substrate and the outersurface of the chuck body, removing heat from the chuck body by heatconductance through the heat transfer gas supplied to the plenum, andprocessing the substrate.

[0017] According to a preferred embodiment, the method further comprisessupplying process gas to the chamber and energizing the process gas intoa plasma and etching an exposed surface of the substrate with the plasmaduring the processing step. However, an exposed surface of the substratecan be coated during the processing step. The process gas can beenergized into the plasma by any suitable technique such as supplyingradiofrequency energy to an antenna which inductively couples theradiofrequency energy into the chamber. During the processing step, thesubstrate can be heated by supplying power to a heater element embeddedin the chuck body. Prior to clamping the substrate, the substrate can belowered onto the outer surface of the chuck body with lift pins mountedon the heat transfer body, the lift pins passing through openings in anouter portion of the chuck body. In order to withdraw heat from thechuck body, the method can include circulating a liquid coolant in theheat transfer body. Temperature changes in the substrate can bemonitored with a temperature sensor supported by the heat transfer bodyand extending through a hole in the chuck body. In the case of plasmaetching a layer of platinum during the processing step, the substratecan be heated to a temperature of over 200° C.

[0018] According to the method, it is possible to achieve a desired heatdistribution across the chuck body by removing heat from the chuck bodythrough multiple heat paths. Further, it is possible to adjust theamount of heat removed through these heat paths by changing the pressureof the heat transfer gas in the plenum. For instance, since the ceramicor metallic tubular extension at a central portion of the underside ofthe chuck body conducts heat from the chuck body to the heat transferbody, the method can include adjusting pressure of the heat transfer gasin the plenum so that heat removed through a first heat path provided bythe heat transfer gas in the plenum balances heat removed through asecond heat path provided by the expansion joint and heat removedthrough a third heat path provided by the tubular extension.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The invention will be described in greater detail with referenceto the accompanying drawings in which like elements bear like referencenumerals, and wherein:

[0020]FIG. 1 shows a cross-section of a vacuum processing chamber inwhich a HTESC assembly of the present invention can be implemented;

[0021]FIG. 2 shows a cross-section of another processing chamber inwhich the HTESC assembly of the present invention can be implemented;

[0022]FIG. 3 shows a perspective view of the cantilevered substratesupport of FIG. 2;

[0023]FIG. 4 shows a cross-section of a HTESC assembly of a firstembodiment of the present invention;

[0024]FIG. 5 shows details of a portion of the HTESC assembly shown inFIG. 4;

[0025]FIG. 6 shows an enlarged view of a portion of the chuck body shownin FIG. 5;

[0026]FIG. 7 shows a cross-section of a HTESC assembly of a secondembodiment of the present invention;

[0027]FIG. 8 shows details of a portion of the HTESC assembly shown inFIG. 6; and

[0028]FIG. 9 shows a cross-section of a portion of a HTESC in accordancewith a third embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] The invention provides an electrostatic chuck useful for clampingsubstrates such as semiconductor wafers during processing thereof in avacuum processing chamber such as a plasma etch reactor. Theelectrostatic chuck, however, can be used for other purposes such asclamping substrates during chemical vapor deposition, sputtering, ionimplantation, resist stripping, etc.

[0030] According to a preferred embodiment of the invention, the chuckincludes a is clamping electrode and an optional heating element whichcan be used to maintain the substrate supported on the chuck at elevatedtemperatures above 80° C. (the upper limit of certain conventionalchucks is 60° C.), preferably over 200° C., for example 250 to 500° C.For example, the chuck can be used to support a wafer during chemicalvapor deposition or plasma etching of materials wherein it is necessaryto heat the substrate to temperatures on the order of about 150° C. andabove. In order to achieve such high temperatures without damage to thechuck, the chuck includes an expansion joint design which provides thechuck with high temperature functionality in a small package.

[0031] According to the preferred embodiment, the expansion jointcreates a plenum between spaced apart surfaces of an actively heatedportion of the chuck and an actively cooled portion of the chuck. Theplenum is filled with a heat transfer gas to conduct heat from theheated portion to the cooled portion of the chuck. With thisarrangement, it is not necessary to use any elastomer seals in theheated portion of the chuck, thereby allowing the heated portion of thechuck to operate at temperatures above which elastomer seals would breakdown. Also, because of the plenum and a heat choke portion of theexpansion joint, the cooled portion of the chuck can be maintained at alow enough temperature to permit use of low cost elastomer seals incontact with surfaces of the cooled portion of the chuck. Moreover, theexpansion joint design provides a small overall height of the chuckwhich makes the chuck compatible with tight system packagingrequirements (footprint). A further advantage of the expansion joint isthat thermal stresses can be accommodated between the heated and cooledportions of the chuck. In addition, a heat transfer gas such as heliumcan be supplied to targeted locations on the underside of the substratewithout the need for a complicated arrangement of gas passages insidethe chuck.

[0032] According to a preferred method of using the chuck according tothe invention, a low volatility etch product can be removed from asubstrate by a plasma etch process wherein the substrate is heated bythe chuck. Such low volatility etch products can be formed during plasmaetching of noble metals such as Pt, Pd, Ru and Ir, materials underconsideration for the electrodes of capacitors using high-k dielectricmaterials. Such low volatility etch products remain on the substratesurface unless the substrate is heated sufficiently. For example,platinum chloride formed during etching of platinum can be volatilizedby heating the substrate to around 300° C. Conventional chucks used mlow temperature etch processes are unsuited for such high temperatureenvironments since they can undergo damaging thermal cycling whichruptures hermetic seals and/or causes failure of chuck materials.Further, because the water cooled portions of such chucks are in directthermal contact with the heated portion of the chuck, the heat from thechuck can cause the cooling fluid to boil and result in uneven coolingof the chuck and/or insufficient cooling of the chuck. The chuckaccording to the invention solves these problems through use of theexpansion joint design.

[0033] According to a preferred embodiment, the chuck body is made froma metallic or ceramic material having desired electrical and/or thermalproperties. For example, the chuck body can be made of aluminum or analuminum alloy. Alternatively, the chuck body can be made from one ormore ceramic materials including nitrides such as aluminum nitride,boron nitride and silicon nitride, carbides such as silicon carbide andboron carbide, oxides such as alumina, etc. with or without fillers suchas particles in the form of whiskers, fibers or the like or infiltratedmetals such as silicon. A ceramic chuck body can be formed by varioustechniques. For instance, the ceramic material can be formed into amonolithic body by a powder metallurgical technique wherein ceramicpower is formed into a chuck body shape such as by compacting or slipcasting the powder with the clamping electrode, heater and power supplyconnections embedded therein, the chuck body being densified bysintering the powder. Alternatively, the chuck body can be formed fromsheets of ceramic material which are overlaid with electricallyconductive patterns for the clamping electrode, the heater and powerfeedthroughs incorporated therein, the layers being cofired to form thefinal chuck body.

[0034] Two embodiments of a high temperature electrostatic chuck (HTESC)assembly according to the invention are now described with reference toFIGS. 1-9. The HTESC assembly offers advantageous features such as hightemperature functionality, relatively low power requirements, longeroperational life, simple backside cooling, lower manufacturing cost andcompact design.

[0035] The HTESC according to the invention can offer better hightemperature functionality and relatively low power requirements comparedto conventional chuck assemblies wherein a cooling plate is integratedas a one-piece electrostatic chuck. In such conventional chuckarrangements, the maximum operational temperature is limited toapproximately 60° C. In order to increase the maximum operationaltemperature, the HTESC of the present invention has been designed as atwo-piece assembly, including an ESC portion such as a ceramic chuckbody having an electrostatic clamping electrode embedded therein and aheat transfer body such as a cooling plate. In addition, an expansionjoint in the form of heat break tubulations have been integrated intothe ESC portion for thermally isolating the ESC portion from the coolingplate. The heat break tubulations significantly reduce conduction ofheat from a peripheral edge of the ESC portion to the cooling plate,thereby allowing the ESC portion to reach temperatures as high asapproximately 500° C. without requiring the supply of a relatively largeamount of power to a heater element embedded in the chuck body.

[0036] The expansion joint provides a long operational life of theHTESC. In particular, by use of the heat break tubulations, the ESCportion can undergo extensive thermal expansion without damaging otherparts of the HTESC. The heat break tubulations can be designed as aone-piece metal part or a multi-piece welded or brazed assembly whichincludes one or more thin-walled sections which allow thermal expansionand contraction of the ESC portion while minimizing heat transfer fromthe ESC portion to the cooling plate. The heat break tubulationsaccommodate differential thermal expansion between the ESC portion andthe cooling plate, thereby minimizing stresses within the HTESC assemblyand thus reducing the chance of premature failure of the HTESC assembly.Furthermore, the heat break tubulations can be designed in a mannerwhich reduces stress at brazed joints within the HTESC assembly.

[0037] Compared to conventional chuck assemblies which rely on acomplicated gas distribution arrangement inside the ESC portion toadequately cool the substrate, the HTESC according to the presentinvention includes a simple arrangement which can selectively targetportions of the substrate where more cooling is desired. For instance,the HTESC assembly includes a plenum between the ESC portion and thecooling plate and the plenum can serve the dual function of (1)withdrawing heat from the ESC portion by supplying a heat transfer gasto the plenum and (2) distributing heat transfer gas to select portionsof the substrate through gas passages extending from the plenum to theouter surface of the ESC portion. In a HTESC used for plasma etching,gas distribution holes can be provided near the outer periphery of theESC portion to enhance the cooling of the outer portion of thesubstrate. Thus, a complicated gas distribution arrangement is notnecessary since the gas distribution holes can be formed by holes atdesired locations in the support surface of the ESC portion.

[0038] Compared to high temperature chuck assemblies which utilizeexpensive metal seals and/or welded bellows arrangements to providevacuum seals, the use of the expansion joint in the HTESC assembly ofthe present invention can reduce manufacturing costs and/or simplifymanufacture of the HTESC. In particular, because the heat breaktubulations thermally isolate the hot ESC portion from the coolingplate, standard low cost elastomer seals can be used at locations incontact with the cooling plate.

[0039] The HTESC according to the invention is designed to provide asmall overall height so that it can be used in vacuum chambers whereinthe chuck is supported on a cantilevered support arm. For example, FIGS.1-3 illustrate examples of vacuum processing chambers 10, 24 into whichthe HTESC assembly of the present invention could be mounted. While theinvention will be explained with reference to the chamber design shownin FIGS. 1-3, it will be appreciated by those skilled in the art thatthe HTESC assembly of the present invention can be used in any vacuumprocessing chamber wherein it is desired to electrostatically clamp asubstrate. For-example, the HTESC assembly of the present inventioncould be used as part of a substrate support in processing chamberswhere various semiconductor plasma or non-plasma processing steps suchas etching, deposition, resist stripping, etc. can be performed.

[0040] As shown in FIG. 1, the vacuum chamber 10 includes a cantileveredsubstrate support 12 extending inwardly from a sidewall of the chamberand a HTESC 14 is supported by the support. A service passage 18containing service conduits (not shown) opens into an interior of thesupport housing 16. The service conduits can be used to service theHTESC, e.g., supply DC power to a clamping electrode, supply RF power tothe clamping electrode or a separate electrode which provides an RF biasto the substrate during processing thereof, supply AC power to a heaterelement, house cables for actuating lift pins, supply coolant forcooling the HTESC and/or the substrate, transmit electrical signals fromsensors or monitoring equipment, etc.

[0041] In the embodiment shown, a mounting flange 20 and support arm 22form an integral piece which can be removably mounted in an opening inthe chamber, e.g., by mechanical fasteners with an O-ring and RFshielding interposed between opposed surfaces of the flange 20 and thechamber. In the arrangement shown in FIG. 1, gas within the chamber canbe withdrawn through an opening 21 by a vacuum pump 23. Plasma can begenerated in the chamber by a source of energy (not shown) mounted atthe top of the chamber. That is, the top of the chamber is designed tosupport various types of plasma generating sources such as capacitivecoupled, inductive coupled, microwave, magnetron, helicon, or othersuitable plasma generating equipment. Also, process gas can be suppliedto the chamber by various types of gas supply arrangements such as a gasdistribution plate (showerhead), one or more gas rings and/or gasinjectors, or other suitable arrangement.

[0042]FIG. 2 illustrates a vacuum processing chamber 24 and acantilevered substrate support 26 on which a chuck assembly 28 has beenmounted. As shown, a substrate 30 is supported on a HTESC assembly 28mounted on a substrate support 26. The substrate support 26 is at oneend of a support arm 32 (shown in FIG. 3) mounted in a cantileverfashion such that the entire substrate support/support arm assembly26/32 can be removed from the chamber by passing the assembly through anopening (not shown) in the sidewall of the chamber 24. Process gas canbe supplied to the chamber by any suitable arrangement such as a gassupply pipe 34 or a gas distribution plate 36 and the gas can beenergized into a plasma state by an antenna 38 such as a planar coilwhich inductively couples Rf energy through a dielectric member 40. Theantenna can be supplied RF energy by any suitable arrangement such as aconventional RF power generator 42 and a match network 44. Duringprocessing of a wafer, a heat transfer gas such as helium can besupplied to the backside of the wafer through holes 46, as shown in FIG.3.

[0043] In the chambers shown in FIGS. 1-3, it is desirable to minimizethe height of the HTESC to allow easy removal of the substrate support26 including the HTESC from the chambers 10, 24. Details of how theHTESC can be made in a compact design will now be explained withreference to the embodiments shown in FIGS. 4-9.

[0044]FIG. 4 shows a HTESC assembly 50 according to a first embodimentof the present invention wherein the HTESC assembly 50 is mounted on acantilevered substrate support 52 in a vacuum processing chamber, asdiscussed above with reference to FIGS. 1-3. The HTESC assembly 50 is atwo-piece design including a chuck body 56 and a heat transfer body 58.The chuck body 56 includes a clamping electrode 60, an optional heaterelement 62, an expansion joint 64, and a central tubular extension 66.The expansion joint 64 includes an annular mounting flange 68 which isremovably attached to the heat transfer body 58 by bolts 70. The chuckbody 56 is preferably made of a ceramic material exhibiting dielectricproperties such as aluminum nitride. The expansion joint 64 and the heattransfer body 58 can be made of heat conducting metals such as aluminum,copper, titanium and alloys thereof, but a preferred material is a lowheat conducting metal such as stainless steel, cobalt, nickel,molybdenum, zirconium or alloys thereof. Alternatively, the expansionjoint 64 and the heat transfer body can be made of any materialscompatible in a vacuum chamber in which semiconductor substrates areprocessed.

[0045] The heat transfer body includes coolant passages and coolant suchas water or other coolant can be supplied to the passages 72 by suitableconduits one of which is shown at 74. Electrical power can be suppliedto the clamping electrode 60 and the heater element 62 by power supplylines in tubular extension 66. For instance, RF and DC power can besupplied to the clamping electrode by a rod 67, the bottom of which isconnected to a strap 69. Temperature of the chuck body can be monitoredwith a temperature feedback assembly 71 in the tubular extension 66.

[0046] A plenum 80 is provided between spaced apart surfaces 82 and 84of the chuck body 56 and the heat transfer body 58. A heat transfer gassuch as helium can be supplied to the plenum 80 by a gas conduit 76. Thetemperature of the substrate on the chuck body can be monitored with afiberoptic element 77 supported in a fitting 78. Although any type oflift pin assembly can be used such as a pneumatically actuated lift pinassembly, according to a preferred embodiment a fitting mounted in abore 79 can be used to support a cable actuated lift pin assembly.Elastomer seals 88 and 90 fitted in grooves in the heat transfer body 58and an elastomer seal 89 fitted in a collar 91 surrounding tubularextension 66 provide vacuum seals between the expansion joint 64 and theheat transfer body 58 and between the tubular extension 66 and the heattransfer body 58. An elastomer seal 92 provides a vacuum seal between anunderside of the heat transfer body 58 and a dielectric mounting plate94 and an elastomer seal 96 provides a vacuum seal between an undersideof the mounting plate 94 and the housing 54. A dielectric edge ring 98(e.g., alumina, silicon nitride, quartz, etc.) overlies the mountingplate 94 and a dielectric focus ring 100 (e.g., alumina, siliconnitride, silicon carbide, etc.) overlies the edge ring 98 and surroundsthe chuck body 56.

[0047]FIG. 5 shows details of the chuck body 56 with the expansion joint64 attached thereto and FIG. 6 is an enlarged view of a brazed joint(detail VI in FIG. 5) between the chuck body 56 and the expansion joint64. As shown in FIG. 5, the expansion joint 64 includes the mountingflange 68, an outer annular section 102, and an inner annular section104, the outer section 102 being connected to the flange 68 by a curvedsection 101 and the inner section 104 being connected to the outersection 102 by a curved section 106. The outer section 102 is separatedfrom the flange 68 by an annular space 108 and the inner section 104 isseparated from the outer section 102 by an annular space 110. The flange68, the outer section 102 and the inner section 104 can be formed (e.g.,machined, cast, forged, etc.) out of a single piece of metal such asstainless steel. Alternatively, the expansion joint can be made from amulti-piece welded or brazed assembly.

[0048] The expansion joint can also include a thin metal ring 112 whichis welded at its bottom to the bottom of the inner section 104 andbrazed at its top to the underside of the chuck body 56. For added jointstrength, a small ceramic ring 114 can be brazed to adjoining surfacesof the chuck body and the ring 112. If aluminum nitride is chosen forthe chuck body, the ring 112 can be of a NiCoFe alloy such as KOVARwhich has a similar coefficient of thermal expansion as aluminumnitride. As shown in FIG. 6, a small gap 116 (e.g., 0.002-0.004 inch) islocated between an inner surface 120 of the inner section 104 and anouter sidewall 122 of the chuck body 56. The ceramic ring 114 is setback from the sidewall 122 such that a gap 118 is provided between thering 112 and the inner section 104, the gap providing sufficient area toaccommodate a brazed joint 124 between the ring 112 and the underside ofthe chuck body 56. If desired, the brazed joint can be replaced with amechanical joint.

[0049] When the chuck body 56 heats up and expands, the sidewall of thechuck body 56 presses against the inner section 104 and elasticallydeflects the inner and outer sections of the expansion joint. As aresult, bending of the ring 112 and consequent stress on the brazedjoint 124 can be minimized. Likewise, less stress is placed on thewelded joint between the ring 112 and the inner section 104. Instead,the curved sections 106 and 110 allow elastic deflection of the innerand outer sections of the expansion joint to accommodate thermalexpansion and contraction of the chuck body 56.

[0050]FIG. 7 shows a HTESC assembly 50′ according to a second embodimentof the present invention wherein the HTESC assembly 50′ is mounted on acantilevered substrate support 52 in a vacuum processing chamber, asdiscussed above with reference to FIGS. 1-3. The HTESC assembly 50′ is atwo-piece design including a chuck body 56′and a heat transfer body 58′.The chuck body 56′ includes a clamping electrode 60′, an optional heaterelement 62′, an expansion joint 64′, and a central tubular extension66′. The expansion joint 64′ includes an annular mounting flange 68′which is removably attached to the heat transfer body 58′ by bolts 70.The chuck body 56′ is preferably made of a ceramic material exhibitingdielectric properties such as aluminum nitride. The expansion joint 64′and the heat transfer body 58′ can be made of heat conducting metalssuch as aluminum, copper, titanium and alloys thereof, but a preferredmaterial is a low heat conducting metal such as stainless steel, cobalt,nickel, molybdenum, zirconium or alloys thereof. Alternatively, thechuck body 56′, the expansion joint 64′ and the heat transfer body canbe made of any materials compatible in a vacuum chamber in whichsemiconductor substrates are processed.

[0051] The heat transfer body 58′ includes coolant passages 72 andcoolant such as water or other coolant can be supplied to the passages72 by conduits one of which is shown at 74. Electrical power can besupplied to the clamping electrode 60′ and the beater element 62′ bypower supply lines in tubular extension 66′. For instance, RF and DCpower can be supplied to the clamping electrode by a rod 67′, the bottomof which is connected to a strap 69′. Temperature of the chuck body canbe monitored with a temperature feedback assembly 71 in the tubularextension.

[0052] A plenum 80 is provided between spaced apart surfaces 82 and 84of the chuck body 56′ and the heat transfer body 58′. A heat transfergas such as helium can be supplied to the plenum 80 by a gas conduit 76.The temperature of the substrate on the chuck body can be monitored witha fiberoptic element 77 supported in a fitting 78. Although any type oflift pin assembly can be used such as a pneumatically actuated lift pinassembly, according to a preferred embodiment a fitting mounted in abore 79 can be used to support a cable actuated lift pin. Elastomerseals 88, 89 and 90 fitted in grooves in the heat transfer body 58′ anda casing 59 bolted to the heat transfer body 58′ provide vacuum sealsbetween the expansion joint 64′ and the heat transfer body 58′ andbetween the tubular extension 66′ and the casing 59. An elastomer seal92 provides a vacuum seal between an underside of the heat transfer body58′ and a dielectric mounting plate 94 and an elastomer seal 96 providesa vacuum seal between an underside of the mounting plate 94 and thehousing 54. A dielectric edge ring 98 (e.g., alumina, silicon nitride,quartz, etc.) overlies the mounting plate 94 and a dielectric focus ring100 (e.g., alumina, silicon nitride, silicon carbide, etc.) overlies theedge ring 98 and surrounds the chuck body 56′.

[0053]FIG. 8 shows details of the chuck body 56′ with the expansionjoint 64′ attached thereto. As shown in FIG. 8, the expansion joint 64′includes the mounting flange 68′, an outer annular section 102′, and aninner annular section 104′, the outer section 102′ being connected tothe flange 68′ by a curved section 101′ and the inner section 104′ beingconnected to the outer section 102′ by a curved section 106′. The outersection 102′ is separated from the flange 68′ by an annular space 108′and the inner section 104′ is separated from the outer section 102′ byan annular space 110′. The flange 68′, the outer section 102′ and theinner section 104′ can be formed (e.g., machined, cast, forged, etc.)out of a single piece of metal such as stainless steel or a multi-piecewelded or brazed assembly of one or more metals such as stainless steel.

[0054] The expansion joint 64′ can also include a thin metal ring 112′which has a flange 113 at its bottom welded to a lip of an extension 105on the bottom of the inner section 104′. The ring 112′ is brazed at itstop to the underside of the chuck body 56′. Alternatively, the ring 112′can be mechanically attached to the chuck body. If aluminum nitride ischosen for the chuck body, the ring 112′ can be of a NiCoFe alloy suchas KOVAR which has a similar coefficient of thermal expansion asaluminum nitride. A small gap 116 (e.g., 0.002-0.004 inch) is locatedbetween an inner surface 120′ of the inner section 104′ and an outersidewall 122′ of the chuck body 56′.

[0055] When the chuck body 56′ heats up and expands, the sidewall 122′of the chuck body 56′ presses against the surface 120′ of the innersection 104′ and elastically deflects the inner and outer sections ofthe expansion joint 64′. As a result, bending of the ring 112′ andconsequent stress on the brazed joint at the top of the ring 122′ can beminimized. Likewise, less stress is placed on the welded joint 115between the ring 112′ and the inner section 104′. Instead, the curvedsections 106′ and 110′ allow elastic deflection of the inner and outersections of the expansion joint 64′ to accommodate thermal expansion andcontraction of the chuck body 56′.

[0056]FIG. 9 shows another HTESC in accordance with the inventionwherein the expansion joint 64″ includes a single annular thin walledsection 126 connected to the mounting flange 68″ by a curved section 127and connected to the chuck body 56″ by a curved section 128. The section126 is separated from the flange 68″ by an annular space 129. Thesubstrate can be raised and lowered with any suitable lift pinarrangement such as a pneumatically actuated lift pin assembly or acable actuated assembly. In the embodiment shown, the lift pin assemblyincludes a plurality of cable actuated lift pins located atcircumferentially spaced apart locations around the periphery of thechuck body 56″. For instance, a plurality of cable actuated lift pinassemblies 130 can be located close to the expansion joint 64″, as shownin FIG. 9.

[0057] The lift pin assembly 130 includes a lift pin 132 which can beraised and lowered by a cable (not shown) attached to a slidable liftpin support 134 in a housing 136. The housing 136 is fitted in the bore86′ so as to maintain a hermetic seal. A further description of suchcable actuated lift pins can be found in commonly owned U.S. Pat. No.5,796,066. The lift pin hole 46′ is sized to allow movement of the pinand heat transfer gas in the plenum 80 can flow around the lift pin 132to the underside of a substrate located in overhanging relationship withthe chuck body 56″.

[0058] The heat transfer gas can be supplied to the plenum 80 through agas passage 138 and the gas in the plenum can be maintained at anysuitable pressure such as 2 to 20 Torr. Depending on the size of thesubstrate, 3 or more lift pins 132 can be used to raise and lower thesubstrate. As shown in FIG. 3, additional holes 46 can be provided toevenly distribute the gas around the edge of the substrate. Further, theholes can open into a shallow groove (not shown) in the upper surface ofthe chuck body to aid in distributing the gas under the substrate. Inorder to provide power to the clamping electrode and the heater element,power supplies 78′ can be provided in the interior of the tubularextension 66″. Also, one of the power supplies 78′ can be used to carryelectrical signals to a substrate temperature sensor (not shown) locatedin the chuck body 56″.

[0059] With the arrangement shown in FIG. 9, the chuck body 56″ canexpand when heated and such expansion can be accommodated by theexpansion joint 64″. The tubular extension 66″ is supported freely abovethe heat transfer body 58″ and due to the clamping pressure created bythe bolted flange 68″, a hermetic seal is maintained between the tubularextension and the heat transfer body 68″ by the elastomer seal 90′.

[0060] The thin cross-section of the annular section or sections of theexpansion joint allows for the thermal isolation of the chuck body fromthe remainder of the HTESC assembly. By thermally isolating the chuckbody and thereby minimizing heat loss due to heat conduction away fromthe chuck body, the chuck body is capable of reaching temperatures ashigh as approximately 500° C. without requiring the expenditure of arelatively large amount of electrical power. In addition, the shape ofthe expansion joint allows the joint to expand and contract as a resultof thermal cycling during processing of a substrate. Accordingly,because thermal stresses on welded and brazed joints of the HTESCassembly are minmized, the HTESC can be expected to have a long workinglife.

[0061] By thermally isolating the chuck body from the rest of the HTESCassembly, standard low cost elastomer materials can be used to formvacuum seals with the heat transfer body. Such vacuum seals can be madefrom a low cost material such as VITON. The chuck body can be made fromcofired layers of ceramic material and metallization layers. Forexample, commonly owned U.S. Pat. No. 5,880,922 describes a suitabletechnique for making a ceramic chuck body. For example, the layers caninclude a conductive layer forming a monopolar or bipolar electrode(which also functions as a RF bias electrode) sandwiched between ceramiclayers. A heater element such as one or more spiral resistance heatingelements can be located between additional ceramic layers. Variousconductive feedthroughs for supplying power to the clamping electrodeand heater element can also be incorporated in the chuck body.

[0062] While the invention has been described in detail with referenceto preferred embodiments thereof, it will be apparent to one skilled inthe art that various changes can be made, and equivalents employed,without departing from the scope of the invention.

What is claimed is:
 1. An electrostatic chuck useful in a hightemperature vacuum processing chamber comprising: a chuck bodycomprising an electrostatic clamping electrode and an optional heaterelement, the electrode being adapted to electrostatically clamp asubstrate on an outer surface of the chuck body; a heat transfer bodyseparated from the chuck body by a plenum located between spaced apartsurfaces of the chuck body and the heat transfer body, the heat transferbody being adapted to remove heat from the chuck body by heatconductance through a heat transfer gas in the plenum; and an expansionjoint attaching an outer periphery of the chuck body to the heattransfer body, the expansion joint accommodating differential thermalexpansion of the chuck body and the heat transfer body while maintaininga hermetic seal during thermal cycling of the chuck body.
 2. Theelectrostatic chuck of claim 1, wherein the heat transfer body comprisesa cooling plate having at least one coolant passage therein in whichcoolant can be circulated to maintain the chuck body at a desiredtemperature, the plenum is an annular space which extends over at least50% of the underside of the chuck body, and the heat transfer bodyincludes a gas supply passage through which heat transfer gas flows intothe annular space.
 3. The electrostatic chuck of claim 1, wherein thechuck body includes gas passages extending between the plenum and theouter surface of the chuck body, the gas passages optionally beinglocated adjacent the expansion joint and supplying heat transfer gasfrom the plenum to the underside of an outer periphery of the substrateduring processing thereof.
 4. The electrostatic chuck of claim 1,wherein the chuck body comprises a metallic material or a ceramicmaterial.
 5. The electrostatic chuck of claim 1, wherein the heattransfer body includes a lift pin arrangement having lift pins movabletowards and away from the chuck body such that the lift pins travelthrough holes in the chuck body to raise and lower a substrate onto andoff of the chuck body.
 6. The electrostatic chuck of claim 1, whereinthe expansion joint includes a mounting flange adapted to be attached tothe heat transfer body and the expansion joint comprises a heat chokewhich includes include inner and outer annular sections interconnectedby a curved section, the inner annular section being attached to thechuck body and the outer annular section being attached to the mountingflange.
 7. The electrostatic chuck of claim 1, wherein the expansionjoint includes a thin ring attached at one end thereof to an outerperiphery of the chuck body by a joint, the ring being of a metal havinga coefficient of thermal expansion close enough to that of the chuckbody to prevent failure of the joint during thermal cycling of the chuckbody.
 8. The electrostatic chuck of claim 1, further comprising aceramic or metallic tubular section extending from a central portion ofthe underside of the chuck body, an outer surface of the tubular sectiondefining a wall of the plenum and the tubular section providing athermal path between the chuck body and the heat transfer body, thetubular extension cooperating with the heat transfer gas in the plenumand the expansion joint to balance heat removed from the chuck body. 9.The electrostatic chuck of claim 8, wherein the interior of the tubularsection includes a power supply supplying RF and DC power supply to theclamping electrode, a power supply supplying AC power to the heaterelement, and/or an arrangement monitoring temperature of the chuck body.10. The electrostatic chuck of claim 4, wherein the chuck body comprisesa ceramic material selected from the group consisting of aluminumnitride, silicon nitride, boron nitride, silicon carbide, boron carbide,alumina or mixture thereof.
 11. The electrostatic chuck of claim 5,wherein the lift pin arrangement comprises a cable actuated lift pinarrangement.
 12. The electrostatic chuck of claim 7, wherein the jointcomprises a brazed joint.
 13. The electrostatic chuck of claim 9,wherein the interior of the tubular section is open to atmosphericpressure.
 14. The electrostatic chuck of claim 1, wherein the expansionjoint includes a thermal expansion section which abuts an outer edge ofthe chuck body, the thermal expansion section being thermally expandibleand contractible to accommodate changes in dimensions of the chuck body.15. An electrostatic chuck for a vacuum processing chamber comprising: achuck body comprising an electrode having an electrical contactattachable to an electrical power supply which energizes the electrodesufficiently to electrostatically clamp a substrate on an outer surfaceof the chuck body; and an expansion joint attached to an outer peripheryof the chuck body, the expansion joint being removably attachable to aheat transfer body such that a plenum is formed between spaced apartsurfaces of the chuck body and the heat transfer body.
 16. Theelectrostatic chuck of claim 15, wherein the chuck body includes gaspassages extending between the plenum and the outer surface of the chuckbody, the gas passages optionally being located adjacent the expansionjoint and supplying heat transfer gas from the plenum to the undersideof an outer periphery of the substrate during processing thereof. 17.The electrostatic chuck of claim 15, wherein the chuck body comprises ametallic material or a ceramic material.
 18. The electrostatic chuck ofclaim 15, wherein the expansion joint includes a mounting flange adaptedto be attached to the heat transfer body and the expansion jointcomprises a heat choke which includes include inner and outer annularsections interconnected by a curved section, the inner annular sectionbeing attached to the chuck body and the outer annular section beingattached to the mounting flange.
 19. The electrostatic chuck of claim15, wherein the expansion joint includes a thin ring attached at one endthereof to an outer periphery of the chuck body by a joint, the ringbeing of a metal having a coefficient of thermal expansion close enoughto that of the chuck body to prevent failure of the joint during thermalcycling of the chuck body.
 20. The electrostatic chuck of claim 15,further comprising a ceramic or metallic tubular section extending froma central portion of the underside of the chuck body, an outer surfaceof the tubular section defining a wall of the plenum and the tubularsection providing a thermal path between the chuck body and the heattransfer body, the tubular section cooperating with the heat transfergas in the plenum and the expansion joint to balance heat removed fromthe chuck body.
 21. The electrostatic chuck of claim 20, wherein theinterior of the tubular section includes a power supply supplying RF andDC power to the clamping electrode, a power supply supplying AC power tothe heater element, and/or an arrangement monitoring temperature of thechuck body.
 22. The electrostatic chuck of claim 15, wherein the plenumis an annular space which extends over at least 50% of the underside ofthe chuck body and the electrode is a monopolar or bipolar electrode.23. The electrostatic chuck of claim 15, wherein the expansion jointincludes a thermal expansion section which abuts an outer edge of thechuck body, the thermal expansion section being thermally expandible andcontractible to accommodate changes in dimensions of the chuck body. 24.The electrostatic chuck of claim 15, wherein the expansion jointincludes a mounting flange attachable to the heat transfer body, a heatchoke attached to the mounting flange, and a thin metal ring attached atone end thereof to the heat choke and at the other end thereof to thechuck body.
 25. The electrostatic chuck of claim 17, wherein the chuckbody comprises a ceramic material selected from the group consisting ofaluminum nitride, silicon nitride, boron nitride, silicon carbide, boroncarbide, alumina or mixture thereof.
 26. The electrostatic chuck ofclaim 15, further comprising a lift pin arrangement mounted on the heattransfer body.
 27. The electrostatic chuck of claim 19, wherein thejoint comprises a brazed joint.
 28. A method of processing a substratein a vacuum process chamber wherein the substrate is electrostaticallyclamped on a chuck body comprising a clamping electrode and an expansionjoint attaching an outer periphery of the chuck body to a heat transferbody such that a plenum is formed between spaced apart surfaces of thechuck body and the heat transfer body, the method comprising: clamping asubstrate on an outer surface of the chuck body by energizing theelectrode; supplying a heat transfer gas to the plenum, the heattransfer gas in the plenum passing through gas passages in the chuckbody to a gap between an underside of the substrate and the outersurface of the chuck body; removing heat from the chuck body by heatconductance through the heat transfer gas supplied to the plenum; andprocessing the substrate.
 29. The method of claim 28, further comprisingsupplying process gas to the chamber, energizing the process gas into aplasma, and etching an exposed surface of the substrate with the plasmaduring the processing step.
 30. The method of claim 28, wherein theprocess gas is energized into the plasma by supplying radiofrequencyenergy to an antenna which inductively couples the radiofrequency energyinto the chamber.
 31. The method of claim 28, wherein an exposed surfaceof the substrate is coated during the processing step.
 32. The method ofclaim 28, further comprising heating the substrate above 100° C. bysupplying power to a heater element embedded in the chuck body.
 33. Themethod of claim 28, further comprising lowering the substrate onto theouter surface of the chuck body with lift pins mounted on the heattransfer body, the lift pins passing through openings in an outerportion of the chuck body.
 34. The method of claim 28, furthercomprising circulating a liquid coolant in the heat transfer body. 35.The method of claim 28, further comprising monitoring temperaturechanges in the substrate with a temperature sensor located in a ceramicor metallic tubular section extending from a central portion of theunderside of the chuck body, the interior of the tubular section beingat atmospheric pressure.
 36. The method of claim 28, wherein thesubstrate is at a temperature of over 80° C. during the processing step.37. The method of claim 28, wherein the substrate is at a temperature ofover 200° C. during the processing step.
 38. The method of claim 28,wherein a layer of platinum is plasma etched during the processing step.39. The method of claim 28, wherein a ceramic or metallic tubularextension extends from a central portion of the underside of the chuckbody and conducts heat between the chuck body and the heat transferbody, the method further comprising adjusting pressure of the heattransfer gas in the plenum so that heat removed through a first heatpath provided by the heat transfer gas in the plenum balances heatremoved through a second heat path provided by the expansion joint andheat removed through a third heat path provided by the tubularextension.